Future mobile deployments will be denser, each base station serving at a time only few users. Such deployments involve a very high level of interference and a very fluctuating traffic.
Submitted as part of the study conducted by 3GPP on small cells deployment, the contribution R1-130946 presents simulation results for the SINR (Signal to Interference and Noise Ratio) distribution in representative conditions. As can be seen in this contribution, in all scenarios the majority of users have an SINR below 10 dB, while in very dense deployments of 10 cells per clusters, the majority of users have an SINR below 5 dB and 40% of users have a negative SINR.
For resolving the situation, the contribution R1-131028 proposes a centralized approach: “The resource coordination could be considered as a centralized approach in that the UEs' CSIs (Channel State Information) from multiple cells or transmission points are collected and processed together. The result of the resource coordination would be forwarded to the individual cells or transmission points. Upon receiving the result of the resource coordination, the eNB would know how the wireless resources can be used for each of its cells. Each eNB would transmit its downlink according to the allocated wireless resources”.
However the centralized approach, including the collection of measurement results from the controlled eNBs (base station in LTE) and UEs (user equipments in LTE), is negatively affected by the backhaul delays that occur in DSL loaded networks, and by the uplink limitations of the backhaul.
A number of interference assessment measurements were defined in LTE standards, for example:
1. RSRP (Reference Signal Received Power) and RSRQ (Reference Signal Received Quality) measurements defined in 3GPP TS 36.214 V11.1.0 (2012-12).
2. CSI reports by the UEs that can be taken as often as every few milliseconds.
By using the X2 collaborative interface defined in 3GPP 36.423 v11.4.0, an eNB can inform, by sending Load Indication message, the power reservation per PRB (Physical Resource Block). There is no information regarding the actual use of the frequency resources.
An eNB can reserve full subframes called ABS (Almost Blank Subframes) to be used at low power or low activity and to inform another eNB over the X2 interface. There is no information regarding the use of the other subframes.